Electrochemical fuel cells convert fuel and oxidant to electricity and reaction product. Solid polymer electrochemical fuel cells generally employ a membrane electrode assembly ("MEA") in which an electrolyte in the form of an ion-exchange membrane is disposed between two electrode layers. The electrode layers are made from porous, electrically conductive sheet material, such as carbon fiber paper or carbon cloth. In a typical MEA, the electrode layers provide structural support to the membrane, which is typically thin and flexible.
The MEA contains an electrocatalyst, typically comprising finely comminuted platinum particles disposed in a layer at each membrane/electrode layer interface, to induce the desired electrochemical reaction. The electrodes are electrically coupled to provide a path for conducting electrons between the electrodes through an external load.
During operation of the fuel cell, at the anode, the fuel permeates the porous electrode layer and reacts at the electrocatalyst layer to form protons and electrons. The protons migrate through the ion-exchange membrane to the cathode. At the cathode, the oxygen-containing gas supply permeates the porous electrode material and reacts at the cathode electrocatalyst layer with the protons to form water as a reaction product.
In conventional fuel cells, the MEA is disposed between two electrically conductive plates, each of which typically has at least one flow passage formed therein. The flow passages direct the fuel and oxidant to the respective electrodes, namely, the anode on the fuel side and the cathode on the oxidant side. In a single cell arrangement, fluid flow field plates are provided on each of the anode and cathode sides. The fluid flow field plates act as current collectors, provide fuel and oxidant to the respective anode and cathode catalytic surfaces, and provide channels for the removal of exhaust fluid streams.
One known method for fabricating an MEA for use in an electrochemical fuel cell, is to use a heat-press to join together the MEA components. A disadvantage of this method is that heat-pressing the entire assembly, which comprises the porous electrode layers, catalyst material and solid polymer electrolyte, subjects each of these components to undesirable mechanical and thermal stresses. Such mechanical and thermal stresses can diminish the performance and lifetime of an MEA in an operating fuel cell. Another disadvantage relates to the suitability of this known method for mass production. The heat-pressing procedure is typically a discontinuous or "batch" process. While the press is being heated, a layered structure comprising electrodes, catalyst layers, and a solid ion-exchange membrane, is typically inserted in a press, pressed therein, and subsequently removed from the press. This conventional batch procedure involves inefficient, costly and time-consuming process control.
German Patent DE 195 09 748 C2, discloses a generic process for producing a composite laminate comprising an electrode material, a catalyst material and a solid electrolyte material. The component materials are arranged on an electrostatically charged surface, and an external heater heats the solid electrolyte material until the upper side of the electrolyte material becomes soft. While the upper side of the electrolyte material is still soft, it is applied under pressure to the catalyst material for bonding the catalyst material to the polymer electrolyte. After the bond has set, the composite laminate is removed from the surface. A problem with this procedure is that the dimensions of the electrostatically charged surface limits the size of the MEA produced. A continuous sheet can not be manufactured according to this method.
Accordingly, there is a need for a continuous process for manufacturing a continuous laminated electrolyte-electrode assembly. A continuous process is desirable to improve efficiency by increasing productivity and the speed of the manufacturing process, thereby reducing production costs.